The invention relates to a microbiological method for producing double-haploid Cucumis sativus plants by culturing haploid plants, which is substantially more effective than the previously known methods.
It is known that haploids are spontaneously formed in cucumbers at low frequencies, less than one haploid embryo usually being formed per thousand seeds (Aalders 1958; J. Hered. 49, 41-44). This frequency occurs in many plants, but it is not enough for application in breeding methods.
It is furthermore known (Truong-Andre, 1988; Proceedings of the Eucarpia congress on cucurbitaceae, AvignonMontfavet May 31-Jun. 1-2, 1988) to grow haploid cucumbers in vitro from extracted unfertilized ovules 2-6 weeks after the female flowers have been pollinated with irradiated pollen (400-600 gy). About 3 viable haploid plants are obtained per 1000 ovules. Accordingly, this method, too, is of only limited value for application in breeding programs.
The seoradic formation of embryos and plants from cucumber anthers was described by Sasser and Lazarte; 1982 Hortscience 17, (1) 88, but the ploidy level was not investigated, and the plantlets were most probably formed from somatic tissue.
Callus cultures were obtained from ovaries and anthers by Dryanovska 1985; Comptes Rendus de l'Academie Bulgare des Sciences 38 (9), and diploid, aneuploid and haploid metaphases were observed. Callus formation is said to originate not only from sexual cells. However, no plants were regenerated. These observations therefore do not contribute to breeding programs.